Purification of the protein crystal from Bacillus thuringiensis by zonal gradient centrifugation

Light-Controlled Selective Collection-and-Release of Biomolecules by an On-Chip Nanostructured Device

The analysis of biosamples, e.g., blood, is a ubiquitous task of proteomics, genomics, and biosensing fields; yet, it still faces multiple challenges, one of the greatest being the selective separation and detection of target proteins from these complex biosamples. Here, we demonstrate the development of an on-chip light-triggered reusable nanostructured selective and quantitative protein separation and preconcentration platform for the direct analysis of complex biosamples. The on-chip selective separation of required protein analytes from raw biosamples is performed using antibody-photoacid-modified Si nanopillars vertical arrays (SiNPs) of ultralarge binding surface area and enormously high binding affinity, followed by the light-controlled rapid release of the tightly bound target proteins in a controlled liquid media. Two important experimental observations are presented: (1) the first demonstration on the control of biological reaction binding affinity by the nanostructuring of the capturing surface, leading to highly efficient protein collection capabilities, and (2) the light-triggered switching of the highly sticky binding surfaces into highly reflective nonbinding surfaces, leading to the rapid and quantitative release of the originally tightly bound protein species. Both of these two novel behaviors were theoretically and experimentally investigated. Importantly, this is the first demonstration of a three-dimensional (3D) SiNPs on-chip filter with ultralarge binding surface area and reversible light-controlled quantitative release of adsorbed biomolecules for direct purification of blood samples, able to selectively collect and separate specific low abundant proteins, while easily removing unwanted blood components (proteins, cells) and achieving desalting results, without the requirement of time-consuming centrifugation steps, the use of desalting membranes, or affinity columns.

A simple method for the separation of Bacillus thuringiensis spores and crystals

A simple new method, for separating Bacillus thuringiensis crystals from spores and cell debris, is described. The developed purification method uses hexane and low speed centrifugation and does not require any expensive material or reagents.

Comparison of Disulfide Contents and Solubility at Alkaline pH of Insecticidal and Noninsecticidal Bacillus thuringiensis Protein Crystals

We compared two insecticidal and eight noninsecticidal soil isolates of Bacillus thuringiensis with regard to the solubility of their proteinaceous crystals at alkaline pH values. The protein disulfide contents of the insecticidal and noninsecticidal crystals were equivalent. However, six of the noninsecticidal crystals were soluble only at pH values of >/=12. This lack of solubility contributed to their lack of toxicity. One crystal type which was soluble only at pH >/=12 (strain SHP 1-12) did exhibit significant toxicity to tobacco hornworm larvae when the crystals were presolubilized. In contrast, freshly prepared crystals from the highly insecticidal strain HD-1 were solubilized at pH 9.5 to 10.5, but when these crystals were denatured, by either 8 M urea or autoclave temperatures, they became nontoxic and were soluble only at pH values of >/=12. These changes in toxicity and solubility occurred even though the denatured HD-1 crystals were morphologically indistinguishable from native crystals. Our data are consistent with the view that insecticidal crystals contain distorted, destabilized disulfide bonds which allow them to be solubilized at pH values (9.5 to 10.5) characteristic of lepidopteran and dipteran larval midguts.

Bacillus thuringiensis HD-73 Spores Have Surface-Localized Cry1Ac Toxin: Physiological and Pathogenic Consequences

Spores from Cry(sup+) strains of Bacillus thuringiensis bound fluorescein isothiocyanate-labeled antibodies specific for the 65-kDa activated Cry 1Ac toxin, whereas spores from Bacillus cereus and Cry(sup-) strains of B. thuringiensis did not. The Cry(sup+) spores could be activated for germination by alkaline conditions (pH 10.3), whereas Cry(sup-) spores could not. Once the surrounding exosporia had been removed or permeabilized, Cry(sup+) spores were able to bind the toxin receptor(s) from insect gut brush border membrane vesicle preparations, and their germination rates were increased ca. threefold in the presence of brush border membrane vesicles. A model is presented whereby in the soil the Cry toxins on the spore surface are protected by the exosporium while in the gut they are exposed and available for binding to the insect receptors. This model explains why the disulfide-rich C terminus of the cry genes is so highly conserved even though it is removed during the processing of the protoxin to the activated toxin. It also highlights the trade-off resulting from having Cry toxins located on the spore surface, i.e., decreased spore resistance versus enhanced insect pathogenesis.

Dissolution and Degradation of Bacillus thuringiensis delta-Endotoxin by Gut Juice Protease of the Silkworm Bombyx mori

The dissolution and degradation of dagger-endotoxin (crystal) of Bacillus thuringiensis subsp. kurstaki strain HD-1 were investigated. Crystals were dissolved in 0.1 M phosphate-carbonate-NaOH buffer at pH > 12. Swelling of crystals occurred in the buffer between pH 10 and 11, and crystals dissolved in the same buffer supplemented with gut juice protease of the silkworm Bombyx mori. The proteolytic dissolution of crystals occurred after a time lag of several minutes in 0.1 M carbonate-NaOH buffer, pH 10.2. The time lag was not observed when crystals were suspended in the buffer for 30 min before the addition of protease. After the dissolution of the crystals and further degradation of the solubilized protein, the appearance of a toxic protein with a molecular weight of 59,000, designated P-59, was observed. Lower-molecular-weight peptides (less than 40,000) showed no toxicity to the silkworm larvae on feeding. Digestion of the 120,000-dalton subunit of the crystal by gut juice protease also produced P-59. These observations suggest the occurrence of a similar process in vivo, i.e., the swelling of crystals due to the alkalinity of gut juice and the production of P-59, dependent on the hydrolysis of swollen crystals by gut juice protease.

Separation of Protein Crystals from Spores of Bacillus thuringiensis by Ludox Gradient Centrifugation

A method is described for the purification of Bacillus thuringiensis protein crystals by Ludox gradient centrifugation. This method is simple, inexpensive, fast, and efficient compared with other techniques. It has been successfully used to purify and characterize the protein crystals from several B. thuringiensis strains.

Selective inhibition of binding of Bacillus thuringiensis Cry1Ab toxin to cadherin-like and aminopeptidase proteins in brush-border membranes and dissociated epithelial cells from Bombyx mori

Binding analyses with denatured epithelial membrane proteins from Bt (Bacillus thuringiensis) demonstrated at least two kinds of proteins, APNs (aminopeptidases N) and cadherin-like proteins, as possible receptors for the Cry1A class of Bt toxins. Two alternative models have been proposed, both based on initial toxin binding to a cadherin-like protein, but one involving APN and the other not. We have used two Bombyx mori strains (J65 and Kin), which are highly susceptible to Cry1Ab, to study the role of these two types of receptors on Cry1Ab toxin binding and cytotoxicity by means of the inhibitory effect of antibodies. BBMVs (brush-border membrane vesicles) of strain J65 incubated with labelled 125I-Cry1Ab revealed a marked reduction in reversible and irreversible binding when anti-BtR175 (a cadherin-like protein) was used for BBMV pre-treatment. By contrast, the anti-APN1 antibody specifically affected the irreversible binding, while the reversible binding component was not affected. This is the first time that binding of Cry1Ab to APN1 and to a cadherin-like protein from BBMVs in solution has been shown. Dissociated epithelial cells from the Kin strain were used to test the inhibitory effect of the antibodies on the cytotoxicity of Cry1Ab. Pre-incubation of the cells with the anti-BtR175 antibody conferred protection against Cry1Ab, but not the anti-APN1 antibody. Therefore our results seem to support the two models of the mode of action of Cry1Ab in Lepidoptera, depending on whether BBMVs or intact dissociated cells are used, suggesting that both pathways may co-operate for the toxicity of Cry1A toxins in vivo.

Expression of a Bacillus thuringiensisdelta-endotoxin cry1Ab gene in Bacillus subtilis and Bacillus licheniformis strains that naturally colonize the phylloplane of tomato plants (Lycopersicon esculentum, Mills)

AIMS

To introduce a cry gene into microorganisms that naturally colonize the phylloplane of tomato plants to improve the persistence of the Cry proteins for controlling a South American tomato moth (Tuta absoluta, Meyrick, 1917).

METHODS AND RESULTS

A cry1Ab gene isolated from a native Bacillus thuringiensis strain (LM-466), showing a relevant activity against T. absoluta larvae, was cloned into the shuttle vector pHT315 (Arantes and Lereclus 1991). The construct was introduced by electroporation into native Bacillus subtilis and Bacillus licheniformis strains, both natural inhabitants of the tomato phylloplane. Western analysis and toxicity assays against the target larvae proved that the successful expression of the gene was accomplished in host bacteria. Recombinant toxin displayed a similar LC50 value in comparison to native donor strain LM-466. Both transformed Bacillus survived for at least 45 days on the tomato leaf surface.

CONCLUSIONS

Plant-associated microorganisms that naturally colonize the phylloplane could be useful as recombinant microbial delivery systems of toxin genes of B. thuringiensis.

SIGNIFICANCE AND IMPACT OF THE STUDY

Modified microorganisms capable of surviving on leaf surfaces for several weeks with insecticidal activity should allow for a reduction in pesticide application.

Isolation and characterization of intracellular protein inclusions produced by the entomopathogenic bacterium Photorhabdus luminescens

Cells of the entomopathogenic bacterium Photorhabdus luminescens contain two types of morphologically distinct crystalline inclusion proteins. The larger rectangular inclusion (type 1) and a smaller bipyramid-shaped inclusion (type 2) were purified from cell lysates by differential centrifugation and isopycnic density gradient centrifugation. Both structures are composed of protein and are readily soluble at pH 11 and 4 in 1% sodium dodecyl sulfate (SDS) and in 8 M urea. Electrophoretic analysis reveals that each inclusion is composed of a single protein subunit with a molecular mass of 11,000 Da. The proteins differ in amino acid composition, protease digestion pattern, and immunological cross-reactivity. The protein inclusions are first visible in the cells at the time of late exponential growth. Western blot analyses showed that the proteins appeared in cells during mid- to late exponential growth. When at maximum size in stationary-phase cells, the proteins constitute 40% of the total cellular protein. The protein inclusions are not used during long-term starvation of the cells and were not toxic when injected into or fed to Galleria mellonella larvae.

Human cell exposure assays of Bacillus thuringiensis commercial insecticides: production of Bacillus cereus-like cytolytic effects from outgrowth of spores

Most contemporary bioinsecticides are derived from scaled-up cultures of Bacillus thuringiensis subspecies israelensis (Bti) and kurstaki (Btk), whose particulate fractions contain mostly B. thuringiensis spores (> 10(12)/L) and proteinaceous aggregates, including crystal-like parasporal inclusion bodies (PIB). Based on concerns over relatedness to B. cereus-group pathogens, we conducted extensive testing of B. thuringiensis (BT) products and their subfractions using seven human cell types. The Bti/Btk products generated nonspecific cytotoxicities involving loss in bioreduction, cell rounding, blebbing and detachment, degradation of immunodetectable proteins, and cytolysis. Their threshold dose (Dt approximately equal.5 times 10(-14)% BT product/target cell) equated to a single spore and a target cell half-life (tLD(50)) of approximately 16 hr. At Dts > 10(4), the tLD(50) rapidly shifted to < 4 hr; with antibiotic present, no component, including PIB-related [delta]-endotoxins, was cytolytic up to an equivalent of approximately 10(9 )Dt. The cytolytic agent(s) within the Bti/Btk-vegetative cell exoprotein (VCP) pool is an early spore outgrowth product identical to that of B. cereus and acting possibly by arresting protein synthesis. No cytolytic effects were seen with VCP from B. subtilis and Escherichia coli. These data, including recent epidemiologic work indicate that spore-containing BT products have an inherent capacity to lyse human cells in free and interactive forms and may also act as immune sensitizers. To critically impact at the whole body level, the exposure outcome would have to be an uncontrolled infection arising from intake of Btk/Bti spores. For humans, such a condition would be rare, arising possibly in equally rare exposure scenarios involving large doses of spores and individuals with weak or impaired microbe-clearance capacities and/or immune response systems.

Method for purification of bacterial endospores from soils: UV resistance of natural Sonoran desert soil populations of Bacillus spp. with reference to B. subtilis strain 168

Endospores of Bacillus spp. were purified from three Sonoran desert soil samples by Chelex extraction and NaBr density gradient centrifugation and their UV resistances compared with that of B. subtilis strain 168. Natural spore populations exhibited tight adherence to soil particles which was not readily overcome by the extraction and purification procedure. It was observed that spores purified from soil exhibited 2-3 fold higher resistance to UV (as measured by the 90% lethal dose, LD90) than did B. subtilis strain 168 grown on NSM, a standard laboratory sporulation medium, and purified by the same extraction procedure. Cultivation of spore-forming bacteria isolated from soil on NSM resulted in production of spores with essentially identical UV resistance as strain 168, suggesting that spore UV resistance is influenced by the environment in which spores are produced.

The Bacillus thuringiensis insecticidal toxin binds biotin-containing proteins

Brush border membrane vesicles from larvae of the tobacco hornworm, Manduca sexta, contain protein bands of 85 and 120 kDa which react directly with streptavidin conjugated to alkaline phosphatase. The binding could be prevented either by including 10 microM biotin in the reaction mixture or by prior incubation of the brush border membrane vesicles with an activated 60- to 65-kDa toxin from Bacillus thuringiensis HD-73. The ability of B. thuringiensis toxins to recognize biotin-containing proteins was confirmed by their binding to pyruvate carboxylase, a biotin-containing enzyme, as well as to biotinylated ovalbumin and biotinylated bovine serum albumin but not to their nonbiotinylated counterparts. Activated HD-73 toxin also inhibited the enzymatic activity of pyruvate carboxylase. The biotin binding site is likely contained in domain III of the toxin. Two highly conserved regions within domain III are similar in sequence to the biotin binding sites of avidin, streptavidin, and a biotin-specific monoclonal antibody. In particular, block 4 of the B. thuringiensis toxin contains the YAS biotin-specific motif. On the basis of its N-terminal amino acid sequence, the 120-kDa biotin-containing protein is totally distinct from the 120-kDa aminopeptidase N reported to be a receptor for Cry1Ac toxin.

Luminal proteinases from Plodia interpunctella and the hydrolysis of Bacillus thuringiensis CryIA(c) protoxin

The ability of proteinases in gut extracts of the Indianmeal moth, Plodia interpunctella, to hydrolyze Bacillus thuringiensis (Bt) protoxin, casein, and rho-nitroanilide substrates was investigated. A polyclonal antiserum to protoxin CryIA(c) was used in Western blots to demonstrate slower protoxin processing by gut enzymes from Bt subspecies entomocidus-resistant larvae than enzymes from susceptible or kurstaki-resistant strains. Enzymes from all three strains hydrolyzed N-alpha-benzoyl-L-arginine rho-nitroanilide, N-succinyl-ala-ala-pro-phenylalanine rho-nitroanilide, and N-succinyl-ala-ala-pro-leucine rho-nitroanilide. Zymograms and activity blots were used to estimate the apparent molecular masses, number of enzymes, and relative activities in each strain. Several serine proteinase inhibitors reduced gut enzyme activities, with two soybean trypsin inhibitors, two potato inhibitors, and chymostatin the most effective in preventing protoxin hydrolysis.

Nonenzymatic Glycosylation of Lepidopteran-Active Bacillus thuringiensis Protein Crystals

We used high-pH anion-exchange chromatography with pulsed amperometric detection to quantify the monosaccharides covalently attached to Bacillus thuringiensis HD-1 (Dipel) crystals. The crystals contained 0.54% sugars, including, in decreasing order of prevalence, glucose, fucose, arabinose/rhamnose, galactose, galactosamine, glucosamine, xylose, and mannose. Three lines of evidence indicated that these sugars arose from nonenzymatic glycosylation: (i) the sugars could not be removed by N - or O -glycanases; (ii) the sugars attached were influenced both by the medium in which the bacteria had been grown and by the time at which the crystals were harvested; and (iii) the chemical identity and stoichiometry of the sugars detected did not fit any known glycoprotein models. Thus, the sugars detected were the product of fermentation conditions rather than bacterial genetics. The implications of these findings are discussed in terms of crystal chemistry, fermentation technology, and the efficacy of B. thuringiensis as a microbial insecticide.

Resistance to Bacillus thuringiensis by the Indian meal moth, Plodia interpunctella: comparison of midgut proteinases from susceptible and resistant larvae

Midgut homogenates from susceptible and resistant strains of the Indian meal moth, Plodia interpunctella, were compared for their ability to activate the entomocidal parasporal crystal protein from Bacillus thuringiensis. The properties of midgut proteinases from both types of larvae were also examined. Electrophoretic patterns of crystal protein from B. thuringiensis subspecies kurstaki (HD-1) and aizawai (HD-133 and HD-144) were virtually unchanged following digestion by either type of midgut homogenate. Changes in pH (9.5 to 11.5) or midgut homogenate concentration during digestion failed to substantially alter protein electrophoretic patterns of B. thuringiensis HD-1 crystal toxin. In vitro toxicity of crystal protein activated by either type of midgut preparation was equal toward cultured insect cells from either Manduca sexta or Choristoneura fumiferana. Electrophoresis of midgut extracts in polyacrylamide gels containing gelatin as substrate also yielded matching mobility patterns of proteinases from both types of midguts. Quantitation of midgut proteolytic activity using tritiated casein as a substrate revealed variation between midgut preparations, but no statistically significant differences between proteolytic activities from susceptible and resistant Indian meal moth larvae. Inhibition studies indicated that a trypsin-like proteinase with maximal activity at pH 10 is a major constituent of Indian meal moth midguts. The results demonstrated that midguts from susceptible and resistant strains of P. interpunctella are similar both in their ability to activate B. thuringiensis protoxin and in their proteolytic activity.

Formation of crystals of the insecticidal proteins of Bacillus thuringiensis subsp. aizawai IPL7 in Escherichia coli

Escherichia coli JM103 cells harboring expression plasmid pTB1 or pKC6 synthesized the 130- and 135-kilodalton insecticidal proteins, respectively, of Bacillus thuringiensis subsp. aizawai IPL7, and both products accumulated as cytoplasmic inclusion bodies. Amorphous inclusions which contained contaminating proteins, together with the corresponding insecticidal proteins, were formed in cultures at 37 degrees C, but bipyramidal crystals practically free of contaminants were observed at 30 degrees C. Although 9.8% of the amino acids were substituted between these two proteins, both protein crystals had the same shape as those of the parental B. thuringiensis strain, which produced both proteins.

The glycoprotein toxin of Bacillus thuringiensis subsp. israelensis indicates a lectinlike receptor in the larval mosquito gut

The mosquito-active protein crystals produced by Bacillus thuringiensis subsp. israelensis contain covalently attached aminosugars which are critical for their larvicidal activity. The 50% lethal concentrations toward Aedes aegypti larvae were increased up to 10-fold by mild periodate treatment, up to 40-fold by forming the protein crystals in the presence of tunicamycin, and up to 7-fold by the presence during the mosquito bioassays of N-acetylglucosamine or its trimer, triacetylchitotriose. Periodate-treated crystals and crystals formed in the presence of tunicamycin had greatly reduced binding capacities for wheat germ agglutinin, an N-acetylglucosamine-specific lectin. These results suggest that the B. thuringiensis subsp. israelensis glycoprotein toxin binds to a lectinlike receptor in the larval mosquito gut. Furthermore, the distinct lectin-binding patterns exhibited by diptera-active versus lepidoptera-active B. thuringiensis crystals suggest that host specificity for the microbial insecticides is determined, in part, by the carbohydrate portion of their glycoprotein crystals.

Purification of the mosquitocidal and cytolytic proteins of Bacillus thuringiensis subsp. israelensis

Two proteins from parasporal crystals of Bacillus thuringiensis subsp. israelensis were purified to electrophoretic homogeneity by gel filtration and anion-exchange chromatography. The larger of the two proteins (molecular weight, 68,000) was not cytolytic, whereas the smaller protein (molecular weight, 28,000) was highly cytolytic when assayed against rat erythrocytes. When these proteins were assayed against larvae of the yellow fever mosquito, Aedes aegypti, the larger protein was at least 100-fold more toxic than the smaller protein. Although proteolytic activity was not detected in solubilized crystals nor in purified protein preparations, the toxin (molecular weight, 68,000) was readily degraded to smaller, nontoxic molecules, even when maintained at 4 degrees C. Mixtures of the two purified proteins were significantly more toxic to mosquito larvae than was either protein alone. Thus, it is likely that both the mosquitocidal and the cytolytic protein play roles in the overall insecticidal action of the parasporal crystal produced by this bacterium.

Cytolytic activity and immunological similarity of the Bacillus thuringiensis subsp. israelensis and Bacillus thuringiensis subsp. morrisoni isolate PG-14 toxins

The parasporal bodies of the mosquitocidal isolates of Bacillus thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni isolate PG-14 were compared with regard to their hemolytic and cytolytic activities and the immunological relatedness of the 28- and 65-kilodalton (kDa) proteins that occur in both subspecies. The alkali-solubilized parasporal bodies of B. thuringiensis subsp. israelensis caused 50% lysis of human erythrocytes at 1.14 micrograms/ml, whereas those of B. thuringiensis subsp. morrisoni caused similar lysis at 1.84 micrograms/ml. Preincubation of solubilized parasporal bodies with dioleolyl phosphatidylcholine significantly inhibited the hemolytic activity of both supspecies. In cytolytic assays against Aedes albopictus cells, the toxin concentrations causing 50% lysis for B. thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni were 1.87 and 11.98 micrograms/ml, respectively. Polyclonal antibodies raised separately against the 25-kDa protein (a tryptic digest of the 28-kDa protein) or the 65-kDa protein of B. thuringiensis subsp. israelensis cross-reacted, respectively, with the 28- and the 65-kDa proteins of B. thuringiensis subsp. morrisoni. However, neither of these antibodies cross-reacted with the 135-kDa protein of either subspecies. These results indicate that the mosquitocidal and hemolytic properties of B. thuringiensis subsp. israelensis and B. thuringiensis subsp. morrisoni isolate PG-14 are probably due to the biologically related proteins that are present in the parasporal bodies of both subspecies. The lower hemolytic activity of the B. thuringiensis subsp. morrisoni may be due to the presence of lower levels of the 28-kDa protein in that subspecies.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino sugars in the glycoprotein toxin from Bacillus thuringiensis subsp. israelensis

The carbohydrate content of purified Bacillus thuriniensis subsp. israelensis crystal toxin was determined by six biochemical tests, column chromatography on an amino acid analyzer, and the binding of 11 fluorescent lectins. The crystals contained approximately 1.0% neutral sugars and 1.7% amino sugars. The amino sugars consisted of 70% glucosamine and 30% galactosamine. No N-acetylneuraminic acid (sialic acid) was detected. The presence of amino sugars was confirmed by the strong binding of fluorescent wheat germ agglutinin and the weak binding of fluorescent soybean agglutinin. These lectins recognize N-acetyl-D-glucosamine and N-acetyl-D-galactosamine, respectively. The lectin-binding sites appeared evenly distributed among the protein subunits of the crystal. The sugars were covalently attached to the crystal toxin because wheat germ agglutinin still bound alkali-solubilized toxin which had been boiled in sodium dodecyl sulfate, separate by polyacrylamide gel electrophoresis, and transferred to nitrocellulose membranes. This study demonstrates the covalent attachment of amino sugars and indicates that the B. thuringiensis subsp. israelensis protein toxins should be viewed as glycoprotein toxins. The crystals used in the present study were purified on sodium bromide density gradients. Studies employing crystals purified on Renografin density gradients can give artificially high values for the anthrone test for neutral sugars.

The biotechnology of Bacillus thuringiensis

One of the challenges in the application of biotechnology to pest control is the identification of agents found in nature which can be used effectively. Biotechnology offers the potential of developing pesticides based on such agents which will provide environmentally sound and economically feasible insect control alternatives. Such an agent, the insect pathogen Bacillus thuringiensis, is the subject of intense investigations in several laboratories. Insecticides which use the entomocidal properties of B. thuringiensis are currently produced and sold worldwide; new products are currently in the development stage. Herein, the biology and genetics of B. thuringiensis and the problems associated with current products are critically reviewed with respect to biotechnology. Moreover, the economic and regulatory implications of technologically advanced products are evaluated.

Trichostrongylus colubriformis: isolation and characterization of ovicidal activity from Bacillus thuringiensis israelensis

Bioassay of media fractions from cultivation of Bacillus thuringiensis israelensis revealed that ovicidal activity for eggs of the ruminant nematode Trichostrongylus colubriformis was found in microbial crystals, but was not released into culture medium. The purified delta-endotoxin of B. t. israelensis, composed of two 25 kDa proteins, had no effect on nematode eggs. A fraction that had high ovicidal activity for eggs of T. colubriformis was isolated by high performance liquid chromatography from crystals of B. t. israelensis. Retention of the compound(s) on size exclusion columns indicated a mol wt of 1510 when compared to standards. The LD50 of this fraction for nematode eggs was not altered significantly by 5 mM calcium chloride with and without ethylenediaminetetraacetic acid or the enzyme inhibitor phenylmethylsulfonyl fluoride (10(-6) M). The fraction was susceptible to proteolytic hydrolysis by bacterial protease VI whereas the fungal protease XIII slightly decreased the ovicidal effects of the fraction. The ovicidal activity was stable for 2 days at ambient temperature or 2 months at 0 C, but declined after 7 days at ambient temperature. Little activity was lost after heating to 100 C for 60 min. The ovicidal effects were also pH dependent with increased toxicity at alkaline pH values. The fraction, however, had no effect on larvae of the mosquito Aedes aegypti or mice after intraperitoneal injection.

Structural similarity between the lepidoptera- and diptera-specific insecticidal endotoxin genes of Bacillus thuringiensis subsp. "kurstaki" and "israelensis"

A gene from Bacillus thuringiensis subsp. "israelensis" was cloned from the large plasmids of this subspecies and was shown to code for a mosquitocidal polypeptide. The gene could be expressed in either Escherichia coli, Bacillus subtilis, or B. thuringiensis subsp. "israelensis" to produce the larvicidal activity. Similarly, a Lepidoptera-specific toxin gene from B. thuringiensis subsp. "kurstaki" was also cloned and expressed in E. coli and B. subtilis. Both cloned genes were sequenced and subjected to computer analysis. A long open translational reading frame coded for the B. thuringiensis subsp. "kurstaki" gene product. However, the B. thuringiensis subsp. "israelensis" clone was composed of two adjacent open reading frames oriented as if they were in a transcriptional operon. The products of the cloned genes retained their specificity for either Lepidoptera or Diptera. The control regions immediately preceding the toxin genes of both B. thuringiensis subspecies showed considerable DNA homology, most likely because both toxins are expressed only during sporulation. In addition, the deduced amino acid sequences from the two contiguous B. thuringiensis subsp. "israelensis" genes bore a striking resemblance to the deduced amino acid sequence from the single larger B. thuringiensis subsp. "kurstaki" gene, as if these two arrangements were evolutionarily related.

Characterization of a parasporal inclusion body from sporulating, enterotoxin-positive Clostridium perfringens type A

Inclusion bodies (IB) synthesized during sporulation and enterotoxin formation by Clostridium perfringens NCTC 8239 and 8798 were isolated and characterized. IB were isolated by disruption of sporangia by sonication in the presence of tetrasodium EDTA and phenylmethylsulfonyl fluoride. Fractionation was carried out in a linear gradient of sodium bromide, sucrose, or diatrizoate sodium. Denaturing and reducing agents were necessary to solubilize the IB. An alkylating agent was required to prevent reaggregation of the subunits. Molecular weight, compositional, and serological analyses and peptide mapping revealed strong similarities between the IB subunits and the enterotoxin synthesized during sporulation by C. perfringens. IB appear to represent the structural component where overproduced enterotoxin accumulates intracellularly. Enterotoxin-like subunits in the IB appeared to be held together by noncovalent and disulfide bonds, which were generally resistant to the action of intracellular proteases of C. perfringens, trypsin, or trypsin plus bile salts.

Isolation of a relatively nontoxic 65-kilodalton protein inclusion from the parasporal body of Bacillus thuringiensis subsp. israelensis

Ultrastructural studies of the mosquitocidal bacterium Bacillus thuringiensis subsp. israelensis revealed that the parasporal body contained three major inclusion types, designated types 1, 2, and 3, which could be differentiated on the basis of electron opacity and size and, to some extent, shape. The type-2 inclusion, which was of moderate electron density and often appeared as a bar-shaped polyhedral body, was isolated on NaBr gradients from purified parasporal bodies and characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transmission electron microscopy, and bioassays against neonate larvae of Aedes aegypti. Purified inclusions averaged 150 to 200 nm by 500 to 700 nm in transverse sections and consisted almost exclusively of a 65-kilodalton (kDa) protein contaminated with minor quantities of 38- and 28-kDa proteins. Lethal concentration values at the 50% level for preparations of the purified parasporal body and the type-2 inclusion were, respectively, 0.66 and 43 ng/ml, indicating that the 65-kDa protein is only slightly toxic to mosquitoes in comparison to the intact parasporal body. Analysis of the type-2 polyhedral inclusion by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and bioassays during different stages of purification demonstrated a positive correlation between the toxicity of the preparation and the degree of contamination with the 28-kDa protein. These results indicate that the 65-kDa protein is not the primary larvicidal toxin, although it may act in conjunction with other parasporal body proteins to produce the high mosquitocidal toxicity characteristic of this bacterium.

Trichostrongylus colubriformis: egg lethality due to Bacillus thuringiensis crystal toxin

A toxin from crystals of Bacillus thuringiensis israelensis was lethal in vitro to eggs of the ruminant nematode Trichostrongylus colubriformis, with an LD50 of 1.8 ng/ml. Larval viability declined after a 2-hr exposure to B. t. israelensis and was dependent on the development period of eggs prior to exposure. Alkaline solubilization suggested that the insecticidal delta-endotoxin of B. t. israelensis was not responsible for nematicidal activity. Filtration of the toxin through 0.2- or 0.45-micron-pore filters revealed that the nematicidal activity was retained on the filter. Toxicity for nematode eggs was decreased by the enzyme inhibitor L-1-tosylamide 2-phenylethylchloromethyl ketone (10(-4) M) or ethylenediaminetetraacetic acid (10(-5) M) and phenylmethylsulfonyl fluoride (10(-6) M). Ethylenediaminetetraacetic acid from 10(-9) to 10(-5) M had no effect on the toxicity while phenylmethylsulfonyl fluoride from 10(-9) to 10(-5) M inhibited toxicity. Fourteen mammalian and microbial enzymes had no significant effect on larval viability while 12 sugars and lipids failed to reduce the toxicity. Addition of 5 mM calcium to the eggs' medium decreased the B. t. israelensis toxicity by 20-fold. The calcium-dependent inhibition of toxicity was reversed by ethylenediaminetetraacetic acid (10(-5) M) and lanthanum chloride (100 microM). The ionophore A-23187 decreased the LD50 by 18-fold to 33.5 ng/ml. Addition of 5 mM calcium chloride to the ionophore and toxin yielded an LD50 of 9.2 ng/ml. Treatment of nematode eggs with B. t. israelensis toxin for 2 or 24 hr had no effect on subsequent binding of selected fluoresceinated lectins to the eggshell.

Nematoda: susceptibility of the egg to Bacillus thuringiensis toxins

Crystalline toxins from Bacillus thuringiensis israelensis and B.t. kurstaki were lethal in vitro to eggs of the nematode Trichostrongylus colubriformis. The LD50 values for the two toxins were 0.38 ng and 37.5 micrograms total protein/ml, respectively. After 1 week at ambient temperature, the LD50 of B.t. kurstaki decreased to less than 4 micrograms/ml. Toxin from B.t. israelensis had no effect within 48 hr on survival of adult nematodes or on their feeding in vitro. Third-stage larvae of T. colubriformis were also unaffected by B.t. israelensis toxin. Exposure of third-stage larvae of Nippostrongylus brasiliensis to 1.1 micrograms total protein/ml of B.t. israelensis for 4 hr had no effect on their infectivity in mice, based on recovery of helminths at 7 days after infection. Similar exposure of 5-day-old N. brasiliensis and subsequent transfer into the intestine of mice gave recoveries that were similar to the untreated control. Thirty strains of B. thuringiensis caused mortality in nematode eggs, but over a 77,000-fold range of activity was found, based on the LD50 values. Toxin from B.t. israelensis was lethal to eggs of six zooparasitic and one free-living species of nematode, but the LD50 values varied 28-fold. Addition of B.t. israelensis to feces that contained eggs of T. colubriformis reduced subsequent recovery of larvae, with an LD50 of 260 ng/g of feces.

Protease activation of the entomocidal protoxin of Bacillus thuringiensis subsp. kurstaki

Two isolates of Bacillus thuringiensis subsp. kurstaki were examined which produced different levels of intracellular proteases. Although the crystals from both strains had comparable toxicity, one of the strains, LB1, had a strong polypeptide band at 68,000 molecular weight in the protein from the crystal; in the other, HD251, no such band was evident. When the intracellular proteases in both strains were measured, strain HD251 produced less than 10% of the proteolytic activity found in LB1. These proteases were primarily neutral metalloproteases, although low levels of other proteases were detected. In LB1, the synthesis of protease increased as the cells began to sporulate; however, in HD251, protease activity appeared much later in the sporulation cycle. The protease activity in strain LB1 was very high when the cells were making crystal toxin, whereas in HD251 reduced proteolytic activity was present during crystal toxin synthesis. The insecticidal toxin (molecular weight, 68,000) from both strains could be prepared by cleaving the protoxin (molecular weight, 135,000) with trypsin, followed by ion-exchange chromatography. The procedure described gave quantitative recovery of toxic activity, and approximately half of the total protein was recovered. Calculations show that these results correspond to stoichiometric conversion of protoxin to insecticidal toxin. The toxicities of whole crystals, soluble crystal protein, and purified toxin from both strains were comparable.

Delta endotoxin of Bacillus thuringiensis subsp. israelensis

From Bacillus thuringiensis subsp. israelensis, a proteinase-resistant protein was purified which exhibited toxicity to larval mosquitoes and cultured mosquito cells, lysed erythrocytes, and was lethal to mice. To extract the protein, a sporulating culture of B. thuringiensis subsp. israelensis was treated with alkali, neutralized, and incubated with trypsin and proteinase K. It was then purified by gel filtration and DEAE column chromatography. Up to 240 micrograms of toxic protein was purified from 1 g (wet weight) of culture pellet. Two closely related forms of toxic protein were obtained: the 25a and 25b proteins. The two forms comigrated near 25,000 daltons in a sodium dodecyl sulfate-polyacrylamide gel, were serologically related, and showed similar partial protease digestion profiles, but were distinguishable by DEAE chromatography and nondenaturing polyacrylamide gel electrophoresis. Protein sequencing data indicated the 25b protein lacked the two amino acids at the amino terminus of the 25a protein. A Western blot enzyme-linked immunosorbent assay of alkali-solubilized proteins that were not treated with proteases suggested the toxic 25a and 25b proteins were proteolytically derived from a larger molecule of about 28,000 daltons. Alkali-solubilized proteins from an acrystalliferous strain of B. thuringiensis subsp. israelensis and from B. thuringiensis subsp. kurstaki failed to cross-react with antibodies to the 25a protein.

Bioassay of solubilized Bacillus thuringiensis var. israelensis crystals by attachment to latex beads

Solubilized crystals of Bacillus thuringiensis var. israelensis were 7000 times less toxic to Aedes aegypti larvae than intact crystals, presumably because mosquito larvae are filter feeders and selectively concentrate particles while excluding water and soluble molecules. A procedure is described whereby soluble toxins are adsorbed to 0.8-micrometer latex beads, with retention of toxicity. The latex bead assay should make it possible to analyze the structure and mode of action of the mosquito toxin.

Two types of entomocidal toxins in the parasporal crystals of Bacillus thuringiensis kurstaki

Two types of entomocidal proteins of Bacillus thuringiensis kurstaki were isolated from the parasporal bodies (crystals), and their structures were compared with each other in relation to the toxic activity. When the crystals were dissociated in 2% 2-mercaptoethanol at pH 10, a protein of Mr = 135,000, called delta-endotoxin, was liberated. The crystals of a strain of B. thuringiensis kurstaki, the HD-1 strain, also released another protein in small quantities. This minor component of HD-1, which had been discovered and named mosquito factor by Yamamoto and McLaughlin (T. Yamamoto and R. E. McLaughlin (1981) Biochem. Biophys. Res. Commun. 103, 414-421) because of its toxicity to mosquito larvae, could be liberated selectively from the crystals by alkali treatment without any thiol reagent at pH 11. Electron microscopic observation suggested that the bipyramidal crystal is composed of a homogeneous component, presumably the delta-endotoxin, and the mosquito factor is not within the crystal matrix. The liberated toxins, including the mosquito factor, were purified by Sephacryl S-300 column chromatography and activated by proteinases obtained from gut juice of the cabbage looper (Trichoplusia ni). The activated toxins were characterized by peptide mapping using techniques of HPLC and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Peptide mapping revealed that the mosquito factor is a protein distinctly different from the delta-endotoxin. Furthermore, a comparison between two strains of B. thuringiensis kurstaki indicated that minor differences in the structure of the delta-endotoxins, in particular the differences in their proteinase-resistant region, caused significant variations in their toxicity to susceptible insects.